This paper shows how continuous hydrothermal synthesis can be scaled up for commercial scale production using a patented reactor design. There are severe limitations with most nanomaterial manufacturing methods not excluding hydrothermal synthesis. Hydrothermal synthesis is limited by the design of reactor that can mix supercritical water with dissolved metal salts without blocking or pre-mixing. The paper shows how the novel reactor was designed by using image analysis to quantify flow patterns in various types of reactor including the traditional t-piece, which is still used at lab scale by many researchers. The t-piece is prone to blocking in the inlet regions and therefore is not a good prospect for scale up. The advantages of hydrothermal synthesis however, include pre-dispersed nanoparticles, 'exotic' chemistries (with mixed metals and doped materials) and good control over particle size. This paper will give examples of materials made for research and commercial purposes using the new reactor. The paper also shows what happens to the mixing regimes in the scaled up version of each potential reactor, with a view to identifying which will most likely be a commercial success.